CommandLine plumbing infrastructure

[ArinGhazarian]

Related to #639

This is all the required infrastructure changes in form of some extension method to do the plumbing for the new CommandLine. Here is a sample branch that applies these changes to bbs2gh.
I went ahead and simplified it even more by creating an extension to add all commands to the rootCommand. Here is how it's supposed to be used:

public static async Task<int> Main(string[] args) // note that Main now returns a Task<int> instead of Task
{
    Logger.LogDebug("Execution Started");
 
    var serviceCollection = new ServiceCollection();
    ... // service registrations
    var serviceProvider = serviceCollection.BuildServiceProvider();

    var rootCommand = new RootCommand("Automate end-to-end Bitbucket Server to GitHub migrations.")
          .AddCommands(serviceProvider);

    ...
}

• Did you write/update appropriate tests
• Release notes updated (if appropriate)
• Appropriate logging output
• Issue linked
• Docs updated (or issue created)

[ArinGhazarian]

Wouldn't it be better to check if handler implements ICommandHander and throw a meaningful exception? It is going to throw a NullReferenceException if GetMethod returns null in case it cannot find BuildHandler method anyways.

[github-actions]

Unit Test Results

0 tests   0 ✔️  0s ⏱️
0 suites  0 💤
0 files    0 ❌

Results for commit bdd4a62.

♻️ This comment has been updated with latest results.

[github-actions]

Integration Test Results

4 tests  ±0   4 ✔️ ±0   14m 46s ⏱️ - 1m 43s
1 suites ±0   0 💤 ±0 
1 files   ±0   0 ❌ ±0 

Results for commit ecc9bdf. ± Comparison against base commit c752c8e.

♻️ This comment has been updated with latest results.

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
Octoshift	89%	75%	854	✔
bbs2gh	73%	65%	261	➖
ado2gh	88%	83%	578	✔
gei	81%	87%	429	✔
Summary	85% (5378 / 6304)	78% (1162 / 1490)	2122	✔